Protection of alternating current systems



NOV. 21, c, R MASON 2.180,990

PROTECTION OF ALTERNATING CURRENT SYSTEMS Filed Sept. 17, 1938 QInventor Charles R Mason,

H is Attorney.

Patented Nov. 21, 1939 2,18%,990

UNITED STATES PATENT OFFICE PROTECTION OF ALTERNATING CURRENT SYSTEMSCharles R. Mason, Schenectady, N. Y., assignor to General ElectricCompany, a corporation of New York Application September 1'7, 1938,Serial No. 230,460

7 Claims. (01. 175-294) My invention relates to improvements in the line6 may operate at a higher or lower voltage protection of alternatingcurrent systems and than the tie line 5. While I have shown the tie moreparticularly to improvements in protective line 6 as only one section inlength, it will be arrangements for alternating current powersysunderstood that either or both tie lines may tenis wherein faults inone zone are likely to comprise one or more sections with intermediateproduce asynchronous conditions in another zone stations. Thus, forexample, the tie line 5 may and thereby cause disturbances to or renderuninclude an intermediate station indicated by the satisfactory theservice to such other zone. polypha e bus The tie lines, as is the usualThere occur in alternating current power syspractice, are provided ateach bus end with suittems arrangements wherein two sources are conablecircuit interrupting means illustrated simply 10 nected by at least twolines, both of which toas latched closed circuit breakers 8, 8, 9, 9',it gether constitute a stronger tie than either one and II of which two,that is 8 and Il, are shown alone. Moreover, one of these ties may carryimfor the purpose of illustrating my invention as v portant loads. Ifthe power limit of this tie is having trip coils l2 although it will beundersuch that asynchronous conditions are likely to stood that theother circuit breakers will in gen- 15 follow disconnection of the othertie on the oceral be similarly equipped. Carried by the tie currence ofa fault thereon, then disruption of line 5 and connected thereto bysuitable circuit service to the important loads results when suchinterrupting means, such as the circuit breakers out-of-step conditionsappear, due to promisl3 and I3, are loads l4 and I4 respectively.

cuous opening of circuit breakers by protective The load I4 may besupplied from the station bus 20 relays responding to such conditions.Moreover 2 and the load l4 connected directly to the the low voltageaccompanying out-of-step conline 5 as shown. The loads may constitutehighly ditions aggravates the situation by causing the important loadsto which continuity of service falling out-of-step of connectedapparatus and is paramount. In fact, each may represent a slowing downof induction motors. whole city network or a highly concentrated in- 25In order to avoid such a breakdown in the much dustrial load. desiredcontinuity of service, I provide in ac- For tie line faults, the circuitbreakers 8, 8,

cordance with my invention means whereby, upon 8, 9, H5 and H will, ingeneral, be controlled by the disconnection of one of the ties from onesuitable fault responsive means, examples of source, to trip only suchcircuit breaker or breakwhich are well known to the art. The load cir-30 ers in the other tie as will minimize the probacult breakers l3 andi3 may also be provided bility of loss of service to any load. Further,with suitable fault responsive means, as is well in accordance with myinvention, I provide means known to the art. However, for the purpose ofwhereby this tripping of breakers in the other illustrating myinvention, I have shown fault tie may follow immediately upon thedisconnecresponsive means for controlling only one of the 35 tion of theone tie or only after it is apparent circuit breakers of the tie line 6,such as II. that asynchronous conditions are about to 00- The tie line5, to which the loads M and [4 our on the other tie if both sources areallowed are connected, will be assumed to have a power to remainconnected in parallel through this other limit such that upondisconnection of the tie line tie. These and other objects of myinvention 6, as by the opening of the circuit breaker H, 40 willhereinafter appearinmore detail. asynchronism between the sources 3 and4 is My invention will be better understood from very apt to occur withan attendant interruption the following description when considered inconin continuity of service to the connected loads. nection with theaccompanying drawing, and its The fault responsive means for effectingthe scope will be pointed out in the appended claims. opening of thecircuit breaker H on the occrr- 45 In the single figure of theaccompanying drawrence of faults on the tie line 6 is illustrated simingwhich diagrammatically illustrates an emply as of the overcurrent faultdetector power bodiment of my invention, two station highvoltdirectional type although it will be obvious that age busses i and2, which are shown as supany other suitable fault responsive means mayplied with alternating current at a desired voltbe employed as far as myinvention is concerned. age by sources 3 and 4 respectively, are con-The fault detectors are illustrated as simple overnected by at least twotie lines 5 and 6. As current relays l5, l6 and I! which have theirshown, one of these lines may operate at a difwindings connected to beenergized by current ferent voltage than the other. Thus, throughtransformers 18, I9 and 28 respectively in the the medium of suitabletransformers l, the tie phase conductors of the tie line 6. As is well55 known to the art, the fault detectors may be simple undervoltagerelays or they may be relays of the so-called distance type in whichresponse is dependent upon both current and voltage so as to insurebetter fault discrimination during both heavy and light load conditionswithout any necessity for changing the relay settings.

The power directional relay ii is illustrated as of the polyphase typehaving current windings 22, 23 and 2 respectively connected to beenergized from the current transformers l8, l9 and 2E] and potentialwindings 25, 2t and 2'! respectively connected to be energized inaccordance with voltages in quadrature with the line currents through asuitable potential transformer 28 connected to be energized from the bus2. For energizing the circuit of the trip coil l2 of the circuit breakerii, the contacts of the fault detectors l5, E6 and H are connected inparallel with each other and in series with the contacts 29 and 313 ofthe power directional relay 2i. As shown, the overcurrent powerdirectional fault responsive means is responsive to faults betweenphases. For ground fault protection, the fault responsive means mayfurther include a ground fault detector and ground fault powerdirectional relay, examples of which are well known to the art.

For the purpose of illustrating my invention, it will be assumed that inthe event that a fault occurs on the tie line 5 that the source 4 is thepreferred source for feeding the load M and that the source 3 alone iscapable of handling the load M when there is any likelihood or certaintyof asynchronism between the sources 3 and t because of theirinterconnection only through the tie line 5 to which the load isconnected. Thus, in accordance with my invention, I arrange, upon theopening of the circuit breaker ii in response to faults on the tie lineto effect the opening of the circuit breaker 8 so as to separate thesources 3 and l. As illustrated, this means comprises aninstantaneous-closing time-delay opening relay 3]! whose winding isconnected in series with the parallel connected contacts of the faultdetectors to, it and if and the contacts 353, 32 of the powerdirectional relay 25. This auxiliary relay may in turn control a circuitto effect the energization of the trip coil E2 of the circuit breaker 8through a time delay closing auxiliary relay 33 which, as shown, closescontacts 34 in a pilot circuit comprising conductors 35 and 3%. As it ispossible that, under certain load conditions or otherwise, asynchronismbetween the sources 3 and t may not occur when the tie line 6 isdisconnected, then in accordance with my invention I may include, in thecontrol circuit of the trip coil E2 of the circuit breaker 8 in series,the contacts of relays 3'4, 38 and 39 which will op crate simultaneouslywhen abnormal conditions afiect' all phases, and thus indicate probableasynchronisrn. As illustrated, these relays are shown as simpleovercurrent relays which are connected to be energized from currenttransformers h), ii and in the phase conductors of the tie line 5 atstation 2. As is well known to the art, these relays may be undervoltagerelays or relays of the overcurrent-undervoltage impedance type ordistance type relays of the power directional voltage restrained type,such as disclosed, for example, in United States Letters Patent1,883,839, issued October 18, 1932. With the impedance or distance typeof fault detector, sensitivity of setting is independent of the load.

If there is little or no probability of maintaining synchronism afterthe disconnection of the tie line *3 from the bus 2, then the relays 31,38 and 3S and also the auxiliary relays 3| and 33 may be omitted and thetripping of the circuit breaker ll effected directly upon the responseof the fault responsive means which controls the circuit breaker llsince there is no need in this case of awaiting any time to ascertainwhether asynchronous conditions are about to occur. While I have assumedconditions such that it is desired to disconnect the tie line 5 at apoint remote from the preferred source l, it is possible that the source3 might be the preferred source in which event some other circuitbreaker might be arranged for tripping. However, where there are two ormore loads M, M connected at different points of the tie line 5, it isdesirable to maintain service to all loads if possible. Consequently itis often preferable to trip an intermediate circuit breaker such as 8instead of an end circuit breaker such as 9 or 3. Also, although I haveshown a pilot circuit for the control of the circuit breaker 3, it willbe obvious to those skilled in the art that this remote control transfertrip could be effected by the use of any transmitted auxiliary current,as carrier current or radio transmission, by suitable arrangements,examples of which are well known to the art.

Assuming the parts positioned as shown in the drawing and that a phasefault occurs on the tie line as indicated by the wavy line 43, then oneor both of the fault detectors it, El and the power directional relay 2!will operate whereby to complete the circuit of the trip coil it throughthe a auxiliary switch 5 4 of the circuit breaker H. Also, through theseries connected contacts of the operated fault detector and the powerdirectional relay ft, the auxiliary relay 3! will be energized to closeits contacts at immediately in the circuit of the time delay closingauxiliary relay 33. This relay will close its contacts 34 after a timesufficient to avoid tripping of the circuit breaker it merely inresponse to a threephase fault on the line 6 which would cause thesimultaneous operation of the relays 3?, 38 and 353. But when theauxiliary relay 3! is deenergized by the opening of the contacts of therelays i5, E6 or ii, and 2| upon the removal of the fault on thetie-line 5, the closed contacts of the instantaneous closing time delayopening relay ti will delay the deenergization of the relay 33 longenough to insure tripping of the circuit breaker ii if the line 5 isasynchronous as indicated by the simultaneous operation of the relaystil, 38 and 3d. Under such conditions the relays 3?, 38, and 39 willclose their serially related contacts 16 in series with the contacts 34of the auxiliary relay 33 whereby to complete the pilot energizingcircuit of the trip coil l2 of the circuit breaker 8 and thus effect theopening thereof.

It will be apparent to those skilled in the art that, if any faultresponsive means, provided to control the branch circuit breakers it and3 to the loads i i and M, is likely to respond to asynchronousconditions, which is very apt to be the case, then it is important inorder to avoid disconnection of the loads and the consequent completeinterruption of service thereto that the circuit breaker 8 should beopened quickly enough to prevent this possibility. Thus in such cases orWhenever a quick interruption of the circuit breaker 3 is required, itis not necessary that the auxiliary relay 33 embody any time delayaction in the closing as this is merely employed as a feeler in thosecases where it is not certain that asynchronism is bound to occur everytime one of the tie lines is disconnected.

While I have shown and described my invention in considerable detail, Ido not desire to be limited to such exact arrangements but seek to coverin the appended claims all those modifications that fall within the truespirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In an electric system comprising two sources of alternating currentinterconn cted by at least two tie lines and a load supplied from one ofsaid tie lines, means for effecting a circuit interruption in the othertie line on the occurrence of a faultthereon including fault responsivemeans energized from said other tie line, and means controlled by saidfault responsive means for effecting the electrical separation of saidsources at a predetermined point in said one tie line. Y

2. In an electric system comprising two sources of alternating currentinterconnected by at least two tie lines and a load supplied from one ofsaid tie lines, means for effecting a circuit interruption in the othertie line on the occurrence of a fault thereon including fault responsivemeans energized from said other tie line, and means for subsequentlyeffecting the electrical separation of said sources at a predeterminedpoint in said one tie line on the occurrence of abnormal conditionssimilarly affecting all phases of said one tie line including meanscontrolled by said fault responsive means.

3. In an electric system comprising two sources of alternating currentinterconnected by at least two tie lines and a load supplied from one ofsaid tie lines, means for effecting a circuit interruption of the othertie line on the occurrence of a fault thereon including fault responsivemeans energized from said other tie line, and means for effecting apredetermined time after the oc currence of the fault on said other tieline the disconnection of one of said sources from said one tie line onthe occurrence of abnormal conditions similarly affecting all phases ofsaid one tie line including means controlled by said fault responsivemeans.

4. In an electric system comprising two sources of alternating currentinterconnected by at least two tie lines and a load supplied from one ofsaid tie lines, one of said sources constituting a preferred source forsupplying said load in the event that abnormal conditions tending toasynchronism appear on said one tie line in consequence of a fault onthe other tie line requiring the interruption thereof, means forefiecting a disconnection of said other tie line from said preferredsource on the occurrence of a fault on said other tie line includingfault responsive means energized therefrom, and means for effecting apredetermined time after the occurrence of the fault on the other tieline the disconnection of said one tie line from the other of saidsources on the occurrence of abnormal conditions similarly affecting allphases of said one tie line including means controlled by said faultresponsive means.

5. In an electric system comprising two sources of alternating currentinterconnected by two tie lines and a load supplied from one of said tielines, one of said sources constituting a preferred source for supplyingsaid loadin the event that abnormal conditions tending to asynchronismappear on said one tie line in consequence of a fault on the other tieline requiring the interruption thereof, means for effecting adisconnection of said other tie line from said preferred source on theoccurrence of a fault on said other tie line including fault responsivemeans energized therefrom, and means controlled by said fault responsivemeans for effecting the discon nection of said one tie line from theother of said sources.

6. A protective arrangement for two parallel tie lines interconnectingdifferent sources of alternating current and having a load connected toone of the tie lines intermediate its ends, comprising means responsiveto a fault on the other of said tie lines for interrupting said othertie line and also said one of said tie lines at a point intermediatesaid load and a predetermined one of said sources.

'7. A protective arrangement for two parallel tie lines interconnectingdifferent sources of alternating current and having a load connected toone of the tie lines intermediate its ends, comprising means responsiveto a fault on the other of said tie lines for interrupting said othertie line, and means for effecting an interruption of said one of saidtie lines at a predetermined point intermediate said load and apredetermined one of said sources on the occurrence of predeterminedasynchronous conditions on said one of said tie lines within apredetermined time after the occurrence of said fault on said other tieline.

CHARLES R. MASON.

